This is not locked in stone. When I last ate low carb, 100 g would move me out of ketosis. It varies from person to person.

You are completely correct there is quite a lot of variation. The 130g Carb is based on averages of regular (couch potatoes) people. My base point I think is valid that you don't want to ride the line between the 2 energy systems due to the potential protein losses.